The processing of polymers and particularly polymers that are polar and/or have an affinity to metal surfaces when melted, can result in build-up of the polymer in the polymer processing equipment (e.g., on a screw or barrel, such as on an extruder, or in a die, an adapter, or other component of the processing equipment). The build-up of polymer, over time, may result in polymer being exposed to heat for an extended period of time (e.g., more than 5 times, or even more than 500 times the average residence time of the polymer in the processing equipment), such that some of the polymer changes in color or flow characteristics. As a consequence, a part being produced using a process that includes a step of processing the polymer through the processing equipment may be discolored, have non-uniform color (e.g., black specks), or have defects resulting from the change in flow characteristics. As one example, polymer that has been exposed to heat for an extended time may result in particles that block the flow of material, such as through a die.
Various methods are known in the art to purge the polymer processing equipment after running a processing resin (i.e., a polymeric material containing one or more polymers), so that the equipment does not need to be dismantled and manually cleaned. The purging may be done with a neat resin or with another processing resin to be processed into parts. Purge compounds are commercially available and are routinely employed to remove certain processing resins. Purge compounds also find utility when transitioning between processing of a first processing resin to a second processing resin.
Purge compounds disclosed in the literature include purge compounds that employ abrasives, foaming agents, surfactants, plasticizers, adhesive components such as polar polymers, to assist in cleaning the polymer processing equipment of certain processing resins. Such purge compounds are described in U.S. Pat. No. 4,731,126 (Dixit et. al., issued Mar. 15, 1988), U.S. Pat. No. 4,838,945 (Fujii et. al., issued Jun. 13, 1989), U.S. Pat. Nos. 5,236,514 (Leung et. al., issued Aug. 17, 1993), 5,424,012 (Ertle et. al., issued Jun. 13, 1995), U.S. Pat. No. 5,443,768 (Scheibelhoffer et. al., issued Aug. 22, 1995), U.S. Pat. No. 5,958,313 Yamamoto et. al., issued Sep. 28, 1999), U.S. Pat. No. 6,060,445 (Chandraker et. al., issued May 9, 2000), U.S. Pat. No. 6,294,120 (Negi et. al., issued Sep. 25, 2001) and U.S. Pat. No. 6,384,002 (Nitzsche, issued May 7, 2002), all of which are expressly incorporated herein in their entirety.
Despite the advances in purge compounds, there continues to be a need for new purge compounds that can purge a broad range of polymers, such that the number of different purge compounds needed by a polymer processor is reduced.
There is also a continued need for purge compounds that purge more efficiently such that the amount of unproductive time on the processing equipment is reduced, the amount of waste generated during the purge is minimized, or both. In particular, there continues to be a need for purge compounds that more efficiently purge polar processing resins, such as polyamides.
As such, there is a need for a new mechanism to purge processing equipment, that can be used alone, or in combination with one or more of the previously described mechanisms (such as abrasion, adhesion, foaming, and the like).